Method For Railway Rolling Stock Unit Center Plate Strengthening And A Device to Perform It

ABSTRACT

The invention relates to the field of metallurgy, in particular to the methods for heat treatment of railway rolling stock parts, specifically railway rolling stock unit center plate. The center plate strengthening device contains a power coil and a sprayer, the power coil being implemented as turnable against the center plate central axis and containing a tube with spray cooling openings. The method for railway rolling stock unit center plate strengthening is performed by progressive induction hardening with simultaneous liquid cooling while rotating the center plate strengthening device  360 ° around the central axis where the center plate treated surfaces undergo induction heating, spray cooling immediately after the heating, and low-temperature volume tempering with a dwelling period.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Russian Patent Application No. 2018118223, filed May 17, 2018, the disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to the field of metallurgy, in particular to the methods for heat treatment of railway rolling stock parts, specifically railway rolling stock unit center plate.

BACKGROUND OF THE INVENTION

The railway rolling stock unit center plate is understood to be a freight car center plate implemented as a detachable unit or as a part of the freight car cast bracket, integral stop, as well as a detachable center plate or center plate arrangement of the freight car coupling assembly.

The surface strengthening of railway rolling stock unit, e.g. a freight car, center plate, cast bracket, integral stop or coupling assembly is required to manufacture the hard layer on the part to significantly reduce wearing of the part working surfaces. The strengthening may be done through the surface heat treatment (hardening).

A method for freight car center plate strengthening by placing on the center plate bearing and thrust surfaces a spring steel bar heat treated to the desired hardness is disclosed (RU 2223166, pub. Feb. 10, 2004).

A technical problem inherent to the above engineering solution is its complexity of implementation caused by additional heat treatment of the bar and fitting the bar on the center plate surface as an interference fit.

In the prior art a method of center plate strengthening by using a plasma torch is disclosed (http://mirprom.ru/public/plazmennaya-zakalka-v-proizvodstve-chast-2.html, FIG. 8). The hardening occurs due to heat transmission into the part body without a water feed to the heated area.

A technical problem inherent to the above engineering solution is its complexity of implementation because the heat source (plasma torch) is small as compared to the surface being hardened, e.g. the center plate bearing surface, and several torch passes are required, which will cause secondary heat impact on the surface sections already treated in the previous passes resulting in the decrease of the hardness of the treated surface.

BRIEF SUMMARY OF THE INVENTION

The technical result of the claimed invention is a simplified process of railway rolling stock unit center plate strengthening by induction hardening of its surface.

The above technical result is achieved by the fact that the method for railway rolling stock unit center plate strengthening, which includes fastening of the center plate against the center plate strengthening device, induction heating of the center plate surfaces being strengthened with subsequent cooling by a coolant carried out by the center plate strengthening device, according to the present invention, is performed by progressive induction hardening with simultaneous liquid cooling while rotating the center plate strengthening device 360° around the central axis, where the center plate treated surfaces undergo induction heating to temperature T within the range of 830-1150° C. and, immediately after the heating, are cooled by spray with coolant flow of 15 to 45 l/min, thereafter low-temperature volume tempering of the part in furnace is performed at 180-250° C. with 1 to 5 hr dwelling period. Full rotation of the center plate strengthening device may be performed within 2-10 minutes. The center plate strengthening device may be located at a distance L from the center plate surface being hardened, within the range of 0.5 to 7 mm. The hardening is performed to a depth of up to 5 mm.

In the center plate strengthening device containing a power coil and a sprayer, according to the present invention, the power coil is implemented as turnable against the center plate central axis and contains a tube with spray cooling openings. The power coil may be implemented as L-shaped. The power coil may contain an additional tube with spray cooling openings. The power coil may be fastened with a clamp so that the power coil axis of rotation is positioned coaxially with the center plate central axis.

BRIEF DESCRIPTION OF THE DRAWINGS

The railway rolling stock unit center plate strengthening device can be explained by the drawings, where:

FIG. 1: shows the device and center plate relative position,

FIG. 2: center plate strengthening device (isometric view),

FIG. 3: center plate strengthening device (view from the side facing the surface being hardened).

DETAILED DESCRIPTION

FIG. 1 shows the relative position of railway rolling stock unit center plate 1 and L-shaped device 2 for its strengthening, located at a distance L from center plate 1 bearing 3 and thrust 4 surfaces. Device 2 is positioned so that it is turnable against center plate 1 central axis 5. Device 2 of the embodiment shown on FIG. 2 is implemented L-shaped and fastened so that its axis of rotation is positioned coaxially with center plate 1 central axis 5, using clamp 6, which in the present embodiment is implemented as two connected thin plates. Device 2 contains a power coil combined with a sprayer, which in the present embodiment is implemented as a bent tube 7 with spray cooling openings 8 (see FIG. 3) facing the center plate surface being hardened. The layout of spray cooling openings 8 depends on center plate 1 size (geometric dimensions). Center plate 1 strengthening device 2 geometry follows the geometry of center plate 1 bearing 3 and thrust 4 surfaces.

The method for railway rolling stock unit center plate strengthening is performed by progressive induction hardening with simultaneous liquid cooling. The center plate strengthening device in the form of a power coil combined with a sprayer is installed coaxially with the center plate at a distance L from the surfaces being hardened, specifically the center plate bearing and thrust surfaces, depending on the center plate size (geometric dimensions). Further, the device is rotated strictly about the center plate axis with constant angular velocity. As the center plate strengthening device rotates around its axis, through the power coil induction heating of the outer layer of the part surface being hardened occurs to temperatures T required for hardening, within the range of 830-1150° C., depending on the grade of steel, of which the rolling stock unit center plate (center plate arrangement) is made. Immediately after the induction heating, spray cooling is performed by a coolant feed to the hardened surface through openings in the power coil tube, with coolant flow of 15 to 45 l/min, depending on the center plate (center plate arrangement) size (geometric dimensions). The spray cooling ensures martensitic and bainitic transformations in the steel to occur. Hardening of the entire center plate (center plate arrangement) working surface occurs as the center plate strengthening device rotates 360°, which is performed within 2-10 minutes, depending on the size (geometric dimensions) of the railway rolling stock unit center plate (center plate arrangement).

After performing the center plate hardening, a low-temperature volume tempering in a furnace is performed at 180-250° C., for residual stress relief, which does not lead to a meaningful impact on the hardness values that resulted from the hardening.

The hardening parameters, such as: time of rotation of the center plate strengthening device, clearances between hardened surface and device, and current intensity and frequency are consistent for the same part sizes, which provides a high degree of repeatability of results, as distinct from the closest prior art. Geometric dimensions of the center plate strengthening device also depend on the center plate (center plate arrangement) size (geometric dimensions).

The implementation of center plate strengthening device as a power coil combined with a sprayer depends on the center plate working surface that requires hardening. However, in most cases, hardening of the center plate bearing and thrust surfaces is performed simultaneously, which significantly simplifies the process of the center plate working surface strengthening due to the L-shape of the center plate strengthening device. Moreover, the implementation of a power coil combined with a sprayer, in particular with a spray cooling tube, provides cooling of the power coil itself during the operation, in addition to cooling the center plate surface being hardened.

The presence of an additional tube with spray cooling openings in the power coil provides accelerated cooling of the heated layer, which is required for martensitic and bainitic transformations in the steel needed to obtain hardened structures responsible for arriving at the desired hardness values of railway rolling stock unit center plate working surface.

For fastening the center plate strengthening device coaxially with the center plate axis, various clamps may be used providing strict coaxial arrangement.

The claimed method for railway rolling stock unit center plate strengthening and the device to perform it simplify the process of center plate strengthening and obtaining the working surface hardness values for center plate arrangements from 375 to 515 HB at the surface, no less than 350 HB at the depth of 3.2 mm from the surface, and no more than 300 HB at the depth of 9.6 mm from the surface. 

1. A method for railway rolling stock unit center plate strengthening, which includes the center plate fastening against the center plate strengthening device, induction heating of the center plate surfaces being strengthened with subsequent cooling by a coolant carried out by the center plate strengthening device, characterized in that it is performed by progressive induction hardening with simultaneous liquid cooling while rotating the center plate strengthening device 360° around the central axis, where the center plate treated surfaces undergo induction heating to temperature T within the range of 830-1150° C. and, immediately after the heating, are cooled by spray with coolant flow of 15 to 45 l/min, thereafter low-temperature volume tempering is performed at 180-250° C. with 1 to 5 hr dwelling period.
 2. The method according to claim 1, characterized in that full rotation of the center plate strengthening device is performed within 2-10 minutes.
 3. The method according to claim 1, characterized in that the center plate strengthening device is located at a distance L from the center plate surface being hardened, within the range of 0.5 to 7 mm.
 4. The method according to claim 1, characterized in that the hardening is performed to a depth of up to 5 mm.
 5. A center plate strengthening device containing a power coil and a sprayer, characterized in that the power coil is implemented as turnable against the center plate central axis and containing a tube with spray cooling openings.
 6. The center plate strengthening device according to claim 5, characterized in that the power coil is implemented as L-shaped.
 7. The center plate strengthening device according to claim 5, characterized in that the power coil contains an additional tube with spray cooling openings.
 8. The center plate strengthening device according to claim 5, characterized in that the power coil is fastened with a clamp coaxially with the center plate central axis. 